[PVE-User] zfs root after last update grub unknown filesystem

[Gianni Milo]

GRUB does not support all zfs features, so it's quite common for it to fail
to recognise the rpool during boot if it has a feature which is
incompatible with it. In your case, I believe that is the "encyption"
feature.
Do you recall the issue starting after enabling encryption on rpool/data
dataset? If so, you may have to rebuild the pool and leave rpool/data
unencrypted.
 Note that even though you enabled encryption only on rpool/data, the
feature will take effect at the pool level, hence the GRUB issue you
are facing.
Because of this issue, people have started using a separate boot pool
(bpool), with limited zfs features enabled and a different data pool
(rpool) for the OS and the data. I believe that the PVE installer should be
modified to follow this approach (if it hasn't done it already) to overcome
similar issues.

Gianni


On Sun, 13 Sep 2020 at 22:29, Stephan Leemburg <sleemburg at it-functions.nl>
wrote:

> Hi All,
>
>
>
> I have a proxmox system at netcup that was clean installed about two
>
> weeks ago.
>
>
>
> It is full zfs, so root on zfs. I am migrating from one netcup system
>
> with less storage to this system.
>
>
>
> This system is using the pve-no-subscription repository, but after
>
> migration I will move the subscription from the 'old' system to this
> system.
>
>
>
> The rpool/data dataset is zfs encrypted.
>
>
>
> Today I did zfs send/recv from the 'old' system to this system to the
>
> rpool/data dataset.
>
>
>
> After that I did an apt update and noticed there where updates available.
>
>
>
> After the upgrade and the mandatory reboot, the system does not come up
>
> anymore. It is stuck in grub rescue.
>
>
>
> Grub mentions that it has a 'unknown filesystem'.
>
>
>
> Has anyone else experienced this same situation?
>
>
>
> If so and you could recover, what was the reason and fix?
>
>
>
> I am still researching what is causing this. If I boot a .iso then I can
>
> import the pool and see all datasets and subvolumes.
>
>
>
> So, it seems that the zpool itself and the datasets are ok, it is just
>
> that grub is unable to recognize them for some reason.
>
>
>
> I have read about other situations like this where large_dnode seemed to
>
> be the cause. I noticed that on the zpool large_dnode is enabled. And it
>
> is a creation only setting. It cannot be changed to disabled afterwards.
>
>
>
> This must have been done by the Proxmox installer. As booting is about
>
> the root filesystem, I guess the zfs send / recv to the rpool/data
>
> dataset would have nothing to do with it, but I could be wrong.
>
>
>
> I will continue my research tomorrow evening after some other
>
> obligations, but if anyone has an idea, please share it. If it is just
>
> how to get more debugging info out of the zfs module in grub.
>
>
>
> Because 'unknown filesystem', with the zfs module loaded is kind of not
>
> helping enough..
>
>
>
> Best regards,
>
>
>
> Stephan
>
>
>
>
>
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